First and foremost, ALWAYS wear proper glasses when shooting anything - handgun, shotgun, whatever. For clay target shooting, you want glasses that make the target stand out against the background, so the color will vary depending on conditions. For example, purple will make orange targets appear very bright. You also do not want glasses that cut out too much light, like very dark sunglasses, as you want your pupils contracted in order to provide the best depth of field. Other than that, try various colors with your particular targets and background to get the most contrast.